mediumMultiple Choice
300-410 Practice Question: Consider the following partial configuration on…
Consider the following partial configuration on router R4:
interface GigabitEthernet0/0 ip address 192.168.2.1 255.255.255.0
ipv6 address 2001:db8:1::1/64 ipv6 ospf 1 area 0 !
interface GigabitEthernet0/1 ip address 10.0.0.1 255.255.255.0
ipv6 address 2001:db8:2::1/64 ipv6 ospf 1 area 0 ! ipv6 router ospf 1 router-id 4.4.4.4
What is the effect of this configuration?
⚠ Common exam trap
Cisco often tests the misconception that OSPFv3 requires an IPv6 router-id, when in fact it uses a 32-bit router-id (like an IPv4 address), and candidates may also incorrectly assume that OSPFv3 needs per-interface router-id configuration or explicit network type statements.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
OSPFv3 will form adjacencies on both interfaces as intended because the router-id is correctly set and OSPFv3 is enabled on each interface.
OSPFv3 (OSPF for IPv6) uses a 32-bit router-id, which can be an IPv4 address (like 4.4.4.4) or any arbitrary 32-bit value, and does not require an IPv6 address. The configuration enables OSPFv3 process 1 under the global 'ipv6 router ospf 1' command, sets the router-id, and activates OSPFv3 on both interfaces with 'ipv6 ospf 1 area 0', allowing adjacencies to form normally on both GigabitEthernet0/0 and GigabitEthernet0/1.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
OSPFv3 will not form adjacencies because the router-id must be an IPv6 address.
Why it's wrong here
OSPFv3 router IDs are 32-bit values written in dotted-decimal notation, so 4.4.4.4 is valid and adjacencies can form. The option confuses router ID format with IPv6 addressing. It is tempting because OSPFv3 runs over IPv6, but the router ID remains an IPv4-style identifier.
- ✗
OSPFv3 will only form adjacency on GigabitEthernet0/0 because the router-id is not configured under the interface.
Why it's wrong here
OSPFv3 sets the router ID from the ipv6 router ospf process command, not per interface, so both GigabitEthernet0/0 and GigabitEthernet0/1 form adjacencies normally. The option is tempting because interface-level router-id exists in OSPFv2, but OSPFv3 has no such requirement.
- ✓
OSPFv3 will form adjacencies on both interfaces as intended because the router-id is correctly set and OSPFv3 is enabled on each interface.
Why this is correct
OSPFv3 enables per interface via ipv6 ospf 1 area 0, and the router-id is explicitly set under ipv6 router ospf 1. Both GigabitEthernet interfaces therefore run OSPFv3 in area 0 and will form adjacencies as intended.
- ✗
OSPFv3 will not form any adjacency because the network type is not specified.
Why it's wrong here
OSPFv3 defaults to broadcast network type on Ethernet interfaces, so adjacencies form without explicit configuration. Specifying network type is only needed on non-broadcast media such as Frame Relay or when overriding the default, which this scenario does not involve.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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Senior Network & Security Engineer · founder of Courseiva
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